This invention relates in general to hand-actuated bicycle brakes, and more particularly to a brake system exhibiting an increase in mechanical advantage over the range of motion of a brake lever.
Bicycle brakes can broadly be classified as handlebar brakes and pedal brakes, depending upon the location where a rider actuates the brakes. As the names suggest, handlebar brakes are actuated at the bicycle handlebar by a rider squeezing a brake handle of a brake lever assembly against the handlebar with his hands, and pedal brakes are actuated at the bicycle pedals. The present invention is an improvement to handlebar brakes.
Numerous types of bicycle brake mechanisms are known in the art, including drum brakes, cantilever brakes, disk brakes, caliper brakes and V-brakes(trademark). One common feature of these brake mechanisms is that the braking force is a function of the force applied to a brake cable extending between the brake mechanism and a brake lever assembly.
Typically a brake lever assembly consists of a brake handle including a finger grip bar and a transverse mounting arm. The mounting arm is attached to the bicycle handlebar (denoted as 100 in FIGS. 6 and 7) by a mounting bracket for pivotal movement relative to the mounting bracket about a fixed axis. The brake cable is attached to the mounting arm at a selected distance from the fixed axis. As the finger grip bar is squeezed by a rider, the mounting arm pivots, increasing the tension on the brake cable, thereby actuating the brake mechanism. Once the brake mechanism is adjusted, the braking force is a function of how hard the finger grip bar is squeezed. How hard the finger grip must be squeezed and how far it must travel to provide a given braking force is known as the xe2x80x9cfeelxe2x80x9d of the brakes.
Bicyclists, particularly avid bicyclists, each have a preferred feel for their bicycle brakes. Riders tend to anticipate the braking force that will result based upon the feel of their brakes. This feel is particularly important in high performance bicycling, such as off-road mountain biking, where applying too much braking force under certain conditions can cause the wheels to lock, resulting in a potentially dangerous loss of rider control. Likewise, too little braking force can have disastrous consequences. Thus, not only is a particular brake feel a matter of user preference, in performance situations a consistent feel contributes to rider safety. To complicate matters, as brake pads wear, the feel of brakes can vary during a ride, particularly during off-road biking where dirt and grit increase brake pad wear and where brakes must be used often and aggressively.
With a conventional brake lever assembly, in order for a bicyclist to obtain desired feel for the handlebar brakes, the brake mechanism itself must be adjusted. This is a time consuming and difficult process requiring special tools. Adjustments are particularly difficult under field conditions where a bicyclist either does not have the necessary tools or does not want to take the time to adjust the brake mechanism.
An alternative known in the art to adjustment to the brake mechanism to alter the brake feel, is providing a structure in the brake lever assembly for varying the perpendicular distance between the fixed axis and the brake cable. This distance is known as the pivot arm. Known prior art devices provide a plurality of holes along the length of the mounting arm at various distances from the fixed axis. While this structure does provide for coarse adjustment of the brake feel, the adjustment is only among pre-selected distances between the fixed axis and the point of attachment of the brake cable. Thus, only a limited number of pivot arm distances, and therefore brake feels, are available. In addition, while this structure does not require disassembly of the brake mechanism to adjust the brake feel, it does require disassembly of the brake lever assembly to reposition the point of attachment of the brake cable to the mounting arm. Thus, adjustment of the brake feel with this structure is time consuming and requires tools which might not be available under field conditions.
Another prior art device employs a slotted lever mounting arm whereby the point of attachment of the brake cable is allowed to transition between varying distances with respect to the fixed axis. Although the noted device provides a varying brake feel, the device also suffers from several drawbacks. The most significant drawback is the abrupt transition of the mechanical advantage and, hence, the force applied to the brake cable. The mechanical advantage is inversely proportional to the pivot arm. The smaller the pivot arm, the greater the power or braking force applied to the brake cable. Therefore, it is crucial that the increase in mechanical advantage be smoothly varying and therefore predictable.
A brake operating device according to one aspect of the invention includes a mounting brake attached to a bicycle handlebar which has a cable guide. A brake lever is pivotally attached to the mounting bracket. One end of the brake cable is routed along the cable guide and is attached to the brake lever at a fixed point, thereby forming an effective cable attachment point. The mounting bracket and the brake lever are configured, and the effective cable attachment point disposed relative to the lever pivot, such that actuation of the brake lever about the lever pivot displaces the cable in a direction transverse to the cable length toward the lever pivot. This provides at least a 33% increase in mechanical advantage over the actuation range of the brake lever from a fully retracted to a fully deflected position.